The present invention relates to an image-receiving sheet for electrophotography, which forms an image excellent in gloss and image quality by an easy method.
The present invention also relates to an image-receiving sheet for electrophotography, which has excellent property of preventing the peeling of a toner image-receiving layer in fixing at a high temperature.
Further, the present invention relates to an image-receiving sheet for electrophotography, which has excellent image quality and gloss and which is protected from the blister formation even in the course of the fixing at a high-temperature.
Image-receiving sheets for electrophotography prepared by forming a polyethylene resin layer in direct contact with the surface of a base paper and forming an image-receiving layer thereon have been known [see, for example, Japanese Patent Unexamined Published Application (hereinafter referred to as xe2x80x9cJ. P. KOKAIxe2x80x9d) No. 2000-10327]. As the fixing temperature is elevated or as the fixing time is prolonged, the gloss and quality of the resultant image are generally improved. In addition, the polyethylene resin layer has a high adhesion to a raw paper. However, its thermal resistance is low and, therefore, when the fixing is conducted at a high temperature, blisters are formed at the interface between the raw paper and the polyethylene resin layer to seriously lower the surface gloss and quality of the image on a toner image-receiving layer formed thereon. For preventing the blister formation, for example, a technique of applying a cross-linking resin such as a polyester or polyurethane to a raw paper and then curing the resin by the radiation is proposed in J. P. KOKAI No. Hei 5-241365. The resin layer cured by the radiation has a high heat resistance. However, it has problems in that the production process thereof is complicated, that a complicated and expensive production equipments are needed, and that the productivity thereof is reduced.
On the other hand, an electrophotographic method is employed for output devices of copying machines and personal computers because in this method, dry treatment is employed, the printing speed is high and general papers (plain papers and wood free papers) are usable. However, when image information such as a face or scenery is to be output as a photograph, a specific photographic paper is necessitated because the general papers are poor particularly in the gloss. For improving the gloss, image-receiving sheets for electrophotography, which comprise a base paper and a toner image-receiving layer containing a thermoplastic resin formed on the support were proposed in J. K. KOKAI Nos. Hei 4-212,168 and Hei 8-211,645. However, glossy electrophotographic image-receiving sheets are designed so that a toner image-receiving layer thereof is improved in the heat response (a phenomenon of sharp melt or softening of the image-receiving layer by the fixing heat) at a low temperature and the fixation. Therefore, these sheets have a problem of so-called blocking. As a result, the following problems are caused: When the electrophotographic image-receiving sheets are stored in piles or in the form of a roll before use, the support of an electrophotographic image-receiving sheet is adhered to the toner image-receiving layer of another electrophotographic image-receiving sheet placed below the support. In another case, the support of an electrophotographic image-receiving sheet is adhered to the toner image-receiving layer of another electrophotographic image-receiving sheet placed below the support and, therefore, when the former sheet is taken out from the pile of the sheets, the toner image-receiving layer is peeled out of the support of the latter sheet. It is effective for solving the blocking problem that fine organic and/or inorganic particles are incorporated into at least one of layers constituting the electrophotographic image-receiving sheet on the toner image-receiving layer side of the support or into the toner image-receiving layer. This method is effective for preventing the blocking. However, it also causes a problem that the gloss of the resultant image is reduced.
Further, image-receiving sheets for electrophotography prepared by forming a polyolefin resin layer on a base paper and forming an image-receiving layer thereon have been known [see, for example, J. P. KOKAI No. 2000-10327]. As the fixing temperature is elevated or as the fixing time is prolonged, the gloss and quality of the resultant image are generally improved. However, as stated above, although the polyethylene resin layer has a high adhesion to a raw paper, its thermal resistance is low and, therefore, when the fixing is conducted at a high temperature, blisters are formed at the interface between the raw paper and the polyethylene resin layer to seriously lower the surface gloss and quality of the image on a toner image-receiving layer formed thereon. This is a problem to be solved. A low density polyethylene (LDPE), a high-density polyethylene (HDPE), etc. are practically used as the polyolefin resins for forming the polyolefin resin layers on both sides of a base paper in Examples in the above-described J. P. KOKAI No. 2000-10327. However, the low-density polyethylenes and high-density polyethylenes can be classified into many grades and their melting points vary in a wide range. Various grades of polyethylenes having different melting points are known.
In addition, the thickness of the polyolefin resin layers is generally referred to in the above-described J. P. KOKAI No. 2000-10327. For example, it is described therein that the thickness of the polyolefin resin layer on the image-receiving layer side is preferably 10 to 60 xcexcm, more preferably 15 to 40 xcexcm (0.015 to 0.40 mm) and that on the back side is preferably 10 to 50 xcexcm (0.010 to 0.050 mm), more preferably 15 to 40 xcexcm (0.015 to 0.40 mm). However, the inventors have found that the blister formation cannot be prevented by only controlling the thickness of the polyolefin resin layer in this range. Namely, the inventors have found that even when only the thickness of the resin layer is controlled in the above-described range, the blister formation cannot be inhibited. In particular, the inventors have found that even when the thickness of the polyolefin resin layer is controlled in this range, the blisters are formed depending on the melting point of the polyolefin resin used and that the blisters are formed particularly in the fixing at a high temperature. The inventors have also found that when an image is formed on the thus obtained image-receiving sheet for electrophotography, the image quality and gloss are lowered.